I'm puzzled as to why the word, vector can mean a direction and magnitude in mathematics, but in biology, it refers to a particular pathogen. The two meanings seem incongruous. Were the biological definition something like, "The pathway taken by a pathogen in spreading infection," it would seem reasonable, but that's not how I've seen it described. Kalleh, since you're in medicine, how do you use it?

Well, Asa, the way I see it is that they are both pathways. In a biological vector, an organism, such as a mosquito or tick, carries disease-causing microorganisms from one host to another, thus providing a pathway for the disease--or a direction for the disease. In mathematics, then, a vector is a quantity, such as velocity, completely specified by a magnitude and a direction; so in a sense, it too provides a pathway. Similarly, in genetics a vector is an agent that transfers genetic material from one cell to another, thus again a pathway. I am much more familiar with biological vectors than mathematical or genetic ones, so I welcome other comments.

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[This message was edited by C J Strolin on Wed Dec 11th, 2002 at 14:56.]

No, CJ, I don't suppose that counts. Do you market your knives like some companies do by cutting a can, or other piece of metal, in half? I have always wondered who would cut metal with kitchen knives anyway!

Asa, a colleague gave me the following explanation that may be better than mine: A vector carries a transmissible disease, and a mathematical vector carries a value, both in a particular direction. Is that better? Mathematical experts, does that work for your vectors? It does for biological/genetic vectors.

In math, according to AHD, a "vector" is a quality, such as speed, that is fully defined by its magnitude and its direction. That is, you can fully define a speed by stating "How fast, and which way?"

It's not clear to me, though, how this parallels the medical definition. The medical meaning seems closer to the etymology.

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[This message was edited by C J Strolin on Wed Dec 11th, 2002 at 14:55.]

Do you market your knives like some companies
do by cutting a can, or other piece of metal, in half? I have always wondered who
would cut metal with kitchen knives anyway!
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You mean, there's ANOTHER way to open a can? Damn! I've been single too long! Well actualy, I do have a pneumatic chisel at work, but that's overkill on a can of beans.

Asa, your last post is a pun waiting to happen, I am sure. Unfortunately, my brain doesn't work that way. Perhaps a dose of your pneumatic chisel would help!

Back to vectors: Shufitz, while direction would definitely fit the vector definition in biology, I agree that magnitude doesn't. Interesting.